LDR SENSOR

Specification

What		Comments
Identifier	LDR
Interface	ADC
Provides	illuminance	lux (*)
Properties	R1 R2	R1 resistance in ohms (**) R2 resistance in ohms (**)

(*)

lux	Surfaces illuminated by
0.0001	Moonless, overcast night sky (starlight)
0.002	Moonless clear night sky with airglow
0.05–0.36	Full moon on a clear night
3.4	Dark limit of civil twilight under a clear sky
20–50	Public areas with dark surroundings
50	Family living room lights
80	Office building hallway/toilet lighting
100	Very dark overcast day
320–500	Office lighting
400	Sunrise or sunset on a clear day
1000	Overcast day: typical TV studio lighting
10,000–25,000	Full daylight (not direct sun)
32,000–100,000	Direct sunlight

(**)

LDR component must be part of a voltage divider circuit:

LDR can be placed in the R1 or R2 location:

• R1 location: R1 = 0, R2 = fixed resistor.
• R2 location: R1 = fixed resistor, R2 = 0.

Typically the fixed resistor is 10K = 10.000 ohms.

Sensor default values are R1 = 10.000 ohms / R2 = 0. Default settings can be changed setting the sensor properties once sensor is attached (see example code).

Code

-- Attach LDR sensor to an external ADC (ADS1115) / channel 0
s = sensor.attach("LDR", adc.ADS1115, 0)

-- Configure sensor. LDR is set on R2, R1 has a fixed value of 10K
s:set("R1", 10000)
s:set("R2", 0)

while true do
  print(s:read("illuminance"))
  tmr.delayms(500)
end

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